seismic response of stratified sites and implications for ... · ahmed elgamal, professor, ucsd....

San Diego Regional Chapter

Workshop: Liquefaction Evaluation, Mapping, Simulation and Mitigation September 12, 2014

Geoffrey R. Martin, Professor Emeritus, USC&

Ahmed Elgamal, Professor, UCSD

Seismic Response of Stratified Sites and Implications for Foundation Systems

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Representative Stratified Site: Liquefaction Design Issues

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Bridges – Lateral Spread Design Issues

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Stratified Sites: Variability of Triggering Factors of Safety

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Historical DevelopmentsLaboratory Simulation of Seismic Loading

Cyclic Simple Shear Stress Induced by Seismic Loading

Seed et al. / Finn et al.1960’s / 1970’s

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Historical Developments

Laboratory Test Results

Representative/Cyclic TriaxialTest Results (Finn, 1971)

Representative/Cyclic Simple Shear Test Results (Peacock and Seed, 1968)

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Stress Controlled Cyclic Simple Shear Tests

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Constant Volume Strain Controlled Cyclic Simple Shear Tests

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Laboratory Tests: Silty Sand – Transitional Behavior

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Effective Stress Site Response Analysis

Finn et.al 1978 : DESRA

Matasovic 1993 : D-MOD

Martin/Qui 1998 : DESRA-MUSC

Pyke 2000 : TESS

Elgamal et.al 2002 : Cyclic/Opensees

Hashash 2009 : DEEPSOIL

Boulanger et.al 2010 : PM4 Sand Model/FLAC

Byrne/Beaty 2011 : UBC Sand/FLAC and PLAXIS

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Plasticity Based Constitutive Models

PM4 Sand Model Boulanger et. al.

Cyclic 1D ModelElgamal et. al.

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Fundamentals Constitutive Model – 1D Effective Stress Site Response Analyses

Computer Programs: DESRA (Lee and Finn, 1978)DESRAMUSC (Qui, 1998)

Objectives:

Time histories of pore water pressure increases in multi layer sites

Determine critical layer for lateral spread analyses

Determine effect of pore water pressure increases on ground surface response

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DESRA Constitutive Model Fundamentals –Cyclic Strain Based Volume Change Parameters

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Input Data for Practical Applications Nonlinear initial τ/γ backbone

curve matched to G/Gmax curve

Masing criteria used tosimulate hysteretic behavior

Strain hardening suppressed

Backbone curve degraded as a function of pore water pressure increase

Representative elastic rebound curves chosen based on N1 values

Volume change parameters (simplified to 2) chosen based on N1 values

Volume change/rebound parameters adjusted to match field liquefaction strength curves

Pore water pressure dissipation/re-distribution during analyses a program option

(Note 𝑚𝑚𝑣𝑣 = 1�𝐸𝐸𝑟𝑟

)

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Example illustrating effects of pore water pressure redistribution and sequential liquefaction

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Stratified Soil Condition at a Bridge Site

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Example illustrating effects of large strain liquefaction

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8th WCEE, 198418

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Elgamal et al. 1989

Site Liquefaction (Soil Liquefaction)

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Adalier and Elgamal 1992


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Kokusho et al. (2000)


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Project VELACS (1993)

(Verification of Liquefaction Analyses by Centrifuge

Studies)

Simple Configurations

Few sensors

Bonnie Silt!


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Fiegel and Kutter 1994

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Boulanger et al. and Kutter et al. 2001-2004

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Figure 4. Geotechnical cross-section for WLA developed from CPT data.

Steidl and Seale 2010

Site Stratification (Wildlife Array, Imperial County, CA)

Youd and Holzer 1994 25

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Cyclic mobility at large shear strain (Zeghal and Elgamal 1994)

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Cyclic mobility at large shear strain (Zeghal and Elgamal 1994)

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Soil Constitutive ModelMulti-yield surface plasticity model (based on Prevost 1985)

Incorporating dilatancy and cyclic mobility effects

Conical yield surfaces for granularsoils (Prevost 1985; Elgamal et al.2003; Yang and Elgamal 2008)

Shear stress-strain and effectivestress path under undrained shearloading condition (Parra 1996, Yang2000, Yang and Elgamal 2002)

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Permeability is a critical parameter for the estimation of liquefaction-induced lateral deformations

Yang, Z. and Elgamal, A. “Influence of Permeability on Liquefaction-Induced Shear Deformation,” Journal of Engineering Mechanics, ASCE, 128, 7, July 2002.

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Before After

1m of Lateral Spreading ( > 3 pile diameters)

NIED, Tsukuba, Japan

Shaking Table Tests: US-Japan Research (UCSD, NSF, NIED, PEER, CALTRANS)5m height: Liquefaction-Induced lateral Spreading Effects on Piles (NIED, Tsukuba)

Professor Kohji Tokimatsu, Dr. Masayoshi Sato, and Dr. Akio Abe

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Shaking Table Tests: US-Japan Research (UCSD, NSF, NIED, PEER, CALTRANS)5m height: Liquefaction-Induced lateral Spreading Effects on Piles (NIED, Tsukuba)Professor Kohji Tokimatsu, Dr. Masayoshi Sato, and Dr. Akio Abe

NIED, Tsukuba, Japan

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Side-view shear

Plan-view shear

around the pile (depends on pile

stiffness)


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OpenSees FE Model

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5.0

LVDT Accelerometer Pore pressure sensor Strain gage

3.8 m 3.9 m 3.9 m----------------------------------- 11.6 m ------------------------------

2 degrees

5.0

mInstrumentation Layout/Experimental Data

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

0.5

1

1.5

2

2.5

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3.5

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4.5

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Ground Lateral Displacement (m)

Depth

(m)

Free-Field Displacement Profile at 10 seconds

NumericalExperimental

Recorded and computed free-field displacement profile at 10 seconds

k= 5 e-5 m/sec

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

0.5

1

1.5

2

2.5

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3.5

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4.5

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Depth

(m)


k = 5 e -5 m/sk = 5 e -4 m/sk = 5 e -3 m/sk = 5 e -2 m/s

Influence of permeability on free-field displacement profile at 10 seconds

1 2 34

1 2 34

(undrained) k1<k2<k3<k4 (drained)

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Influence of permeability on stiff pile moment profile at 10 seconds

-20 0 20 40 60 80 100 120 140 160 180

-1

0

1

2

3

4

5

Moment (kN·m)

Depth

(m)

Stiff Pile Moment Profile at 10 seconds


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

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Depth

(m)



1

1

2

234

34

Free-Field Displacement

1 2 34

(undrained) k1<k2<k3<k4 (drained)

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Conclusion-Permeability is a critical parameter for the estimation of liquefaction-induced lateral deformations- Permeability is a critical parameter for the estimation of pile moments due to liquefaction-induced lateral ground deformation- Larger ground displacement is not always proportional to higher moment in piles

Yang, Z. and Elgamal, A. “Influence of Permeability on Liquefaction-Induced Shear Deformation,” Journal of Engineering Mechanics, ASCE, 128, 7, July 2002 44

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For Saturated Cohesionless soils…

Shear resistance depends on:

1) N1(60) , CPT qc1 , Vs

2) Soil/System Permeability k

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http://soilquake.net/openseespl/

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OpenSeesPL: http://soilquake.net/openseespl/

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OPENSEESPL Example Input Files (http://soilquake.net/openseespl/example_input_files/

Pile in Ground Strata 3-D Shear Beam Site Amplification48

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http://soilquake.net/openseespl/example_input_files/


Ground Modification by Stone Columns. Pile-pinning, Earthquake Drain, or Deep Soil Mixing Grids

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Pile Groups and Piled Rafts


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seismic response of stratified sites and implications for ... · ahmed elgamal, professor, ucsd....

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